Sivers Asymmetries for Inclusive Pion and Kaon Production in Deep-Inelastic Scattering

TL;DR

This paper calculates Sivers distribution functions using diquark models to explain single-spin asymmetries in pion and kaon production during deep-inelastic scattering, aligning well with experimental data and indicating quark orbital angular momentum.

Contribution

It introduces a model-based calculation of Sivers functions incorporating final-state interactions, providing predictions that match experimental results and suggest quark orbital motion.

Findings

Good agreement with HERMES data for pi+ production

Qualitative agreement for pi0 and K+ production

Predictions for future COMPASS measurements

Abstract

We calculate the Sivers distribution functions induced by the final-state interaction due to one-gluon exchange in diquark models of nucleon structure, treating the cases of scalar and axial-vector diquarks with both dipole and Gaussian form factors. We use these distribution functions to calculate the Sivers single-spin asymmetries for inclusive pion and kaon production in deep-inelastic scattering. We compare our calculations with the results of HERMES and COMPASS, finding good agreement for pi+ production at HERMES, and qualitative agreement for pi0 and K+ production. Our predictions for pion and kaon production at COMPASS could be probed with increased statistics. The successful comparison of our calculations with the HERMES data constitutes prima facie evidence that the quarks in the nucleon have some orbital angular momentum in the infinite-momentum frame.